Conventional drums or capstans used for such a windup are generally solid with only a slight degree of elasticity, e.g. when made from foam polystyrene. Their diameters are not adjustable so that fibers wound thereon always retain their initial tension. This is sometimes undesirable, as where tests on tensile strength are to be performed under a modified stress. In many instances it would also be useful to reduce that tension to zero so that a fiber package wound on the drum could be slid off axially for storage as a skein.